EL PASO -- Mexican authorities said the seven bullets that pierced the walls of El Paso City Hall on Tuesday could have been fired by Mexican federal agents.

Federal police spokesman José Ramón Salinas said that six agents stopped a vehicle Monday afternoon to inspect it and that the driver and passengers attacked the agents. A shootout erupted, and a federal agent and a woman were killed.

Salinas said the fact that the vehicle the agents had stopped was later found with bullet holes and blood showed that federal agents had fired shots. Salinas said these findings were preliminary because the shootout is still under investigation by the Chihuahua state attorney general's office.

"The order is always to avoid firing, but the police officer is the one who makes the decision at the moment," Salinas said.

Generally, criminals in Juárez have been using the AK-47 rifles, or what they call "cuerno de chivo," Spanish for goat's horn, because the ammunition clip curves like a horn.

But Salinas said some federal police officers are also armed that type of gun. It fires a round that can easily reach El Paso from Juárez.

No Mexican agency, however, is taking responsibility for the bullets that hit City Hall.

El Paso police do not know the origin of the bullets yet.

Police Chief Greg Allen said Thursday at a news conference that he has not sent the two bullets found at City Hall to a lab for ballistics testing.

Tela Mange, spokeswoman for the Department of Public Safety, said the DPS will test the bullets at one of its 13 ballistics labs. There is a lab in El Paso.

Allen said the commander in charge of the local DPS office offered to expedite the ballistics tests on the bullets. Normally, a ballistics test takes two weeks. But even after the test is done, the department still will not know who the shooter was, Allen said.

"Ballistics aren't going to have any measure of assistance on this type of situation until we actually have the weapon that fired that particular round," he said.

Allen said the bullets found are consistent with the type of bullets Chihuahua state police collected from the shootout in Juárez.

Allen said there is a consensus among law enforcement and government officials that the bullets originated in Juárez even though the theory "is still speculative to a large degree."

City Hall is about 800 to 1,000 yards from the site of the shooting in Juárez. No one was hurt on the U.S. side.

Because the shooting crossed international boundaries, Mexican authorities reached out to El Paso police.

Allen said he has been talking to the Mexican consul general in El Paso about the shooting.

Adrián Sosa, spokesman for the Mexican Consulate in El Paso, said the office has been in contact with both El Paso police and Chihuahua state police to share information about the City Hall bullets.

"Authorities in Mexico are offering to help in any way they possibly can, but we believe that this particular incident will be like the rest of murders in Mexico right now -- unsolvable," Allen said.

Allen said he was surprised it had taken so long for an incident like this to happen in El Paso.

In Juárez, daytime shootings, mutilations, ambushes on police and attacks on government leaders have become common.

Nearly 1,400 people have been murdered in Juárez this year while a war between the Juárez and Sinaloa drug cartels continues.

The violence has hit close to El Paso before.

In September 2009, a man was kidnapped in Horizon City and his mutilated body was found in Juárez. His hands were cut off and placed on his chest, a sign that he was considered a thief.

In mid-March, two U.S. citizens with ties to the U.S. Consulate in Juárez were shot dead.

And most recently, on June 7, a 15-year-old Juárez boy was shot and killed by a U.S. Border Patrol agent.

El Paso Mayor John Cook raised concerns about the violence in the "sister city" at the State of the City address on Thursday.

"We need peace on the other side," he said.

The daily attacks in Juárez have also attracted national attention in both Washington, D.C., and Mexico City.

President Barack Obama announced in June that he would send 1,200 National Guard soldiers to the U.S. border.

Cook said he does not think sending soldiers is the right move for El Paso.

"What are they going to do? Jump up in the air and catch the bullets?" he asked rhetorically. "I'm very concerned about the militarization of the border."

Chief Allen said he would not like to see soldiers on the border.

"I don't think that's the route to go," he said. "I think, right now, we have a dedicated agency, namely the Border Patrol and ICE (Immigration and Customs Enforcement), in place and they should be beefed up before the utilization of military on the border."

Rep. Silvestre Reyes, D-Texas, said the troops are temporary.

"In the short term, they can assist the Border Patrol in a support-role capacity to ensure that all available agents can be focused on keeping the border secure," Reyes said Thursday.

Allen said the U.S. government has failed to find a solution to the violence. Many politicians visit El Paso and promise change to protect Americans, he said.

"They fly out, and we never hear from them again, and it's getting a little bit old," Allen said. "Quite frankly, if a U.S. citizen is killed due to the neglect of the federal government, then something is wrong with the big picture."

Maggie Ybarra may be reached at mybarra@elpasotimes.com; 546-6151.

Adriana Gómez Licón may be reached at agomez@elpasotimes.com; 55466129.